1. Technical Field
The present invention relates to a driving method for driving an electrophoretic display apparatus, a control circuit for executing the driving method, and an electrophoretic display apparatus.
2. Related Art
Well-known examples of reflective devices functioning as a tool for allowing users thereof to read characters displayed thereon include electronic paper displays. Such an electronic paper display is provided with a memory-type display system and has a characteristic of consuming electricity only when updating display content, but consuming the least amount of electricity while retaining the updated display content after the update.
Known examples of such a memory-type display system of this electronic paper display include electrophoretic display systems which have become most popular in recent years. Such an electrophoretic display system has electrophoretic elements each provided therein with microcapsules each encapsulating therein electrically-charged black or white particles, and has a plurality pairs of electrodes, each pair consisting of two electrodes which are located above and below a corresponding electrophoretic element, respectively. This electrophoretic display system causes each pair of the electrodes to be subjected an electric-potential difference therebetween and attract the black-color particles and the white-color particles, and displays a relevant image by configuring aggregates of the black-color particles and aggregates of the white-color particles.
To date, an active matrix method utilizing thin film transistors (TFTs) has been employed as one of driving circuits for driving such an electrophoretic display system.
A driving method according to JP-A-2002-116733 causes an electrophoretic display apparatus to display relevant images by supplying electrophoretic elements, which correspond to respective pixels implemented in relation to the active matrix method, with corresponding voltages during a period of time in accordance with gray-scale values indicated by image data.
However, such an existing driving method for driving an electrophoretic display apparatus has a disadvantage in that, some of pixels having been supplied with corresponding voltages during the same period of time result in displaying an image with variations of gray-scale levels because of influences from surrounding pixels.
Specifically, in an existing driving method, as shown in FIG. 15A, among three juxtaposed pixels 20a, 20b and 20c, focusing the centrally-positioned pixel 20b (an pixel electrode 22b) which is supplied with a blackening voltage (VH), a desired black-color gray-scale level is assured because the pixel electrodes 22a and 22c, which are located at left and right sides adjacent to the pixel electrode 22b, respectively, are supplied with the same voltage VH, and thus, no leakage of unwanted electric fields arises. In addition, a diagram in an upper portion of FIG. 15A is a plan view resulting from viewing the three juxtaposed pixels from a front side, and a diagram in a lower portion thereof is a side cross-sectional view of the three pixels.
On the other hand, as shown in FIG. 15B, the pixel electrodes 22a and 22c, which are located at left and right sides adjacent to the centrally-positioned pixel 20b (an pixel electrode 22b) supplied with a blackening voltage (VH), are supplied with a voltage having a reverse polarity (VL: for example, a whitening voltage). In this case, as shown in a side cross-sectional view in a lower portion of FIG. 15B, an electric potential arising between the adjacent electrodes 22a and the electrode 22b and another electric potential arising between the adjacent electrode 22c and the electrode 22b cause electric fields (denoted by outline arrows) at portions bordering the adjacent pixel electrode 22a and the adjacent electrode 22c, respectively, so that white-color electrically-charged particles 27 are partially moved to the display side, and the centrally-positioned pixel 20b results in displaying an image having slightly whitened black-color gray-scale level compared with a desired black-color gray-scale level.
This phenomenon is considered to be due to existence of pixels which are located at positions surrounding a certain pixel naturally expected to have a desired black-color gray-scale level, and which have gray-scale levels different from the gray-scale level of the certain pixel.
That is, existing driving methods for driving an electrophoretic display apparatus have a disadvantage in that it is difficult to achieve desired display quality.